ECG equipment includes devices or systems that obtain electrical signals (“ECG signals”) representative of electrical signals generated by a patient's heart beat, and provide a visual output of the signal waveform (“ECG waveform”). ECG equipment is useful to medical professionals in detecting anomalies in a patient's ECG waveform caused by abnormal and/or potentially dangerous cardiac conditions. ECG equipment also can detect and display respiration signals generated by the respiratory activity of a patient.
Because of the vital importance of ECG equipment, it is necessary from time to time to test the operation of the equipment. To this end, it is known to provide ECG signal simulators or generators that approximate a human ECG signal. Because the simulated signal has a predetermined heart rate and waveform shape, it may be used to test the ECG equipment. To test the equipment, the leads from the ECG equipment that normally attach to the patient are instead attached to terminals on the ECG signal simulator. The ECG equipment output is then compared to the settings of the ECG signal simulator to ensure that the ECG equipment is properly detecting the heart rate (i.e. pulse), displaying the ECG waveform properly, and/or displaying respiration signals properly.
Moreover, the healthy human heartbeat involves several different signal elements. Accordingly, the ECG waveform associated with a single heartbeat has various regions or features. The ECG signal simulator preferably approximates such features, so that when the ECG equipment is connected to the ECG signal simulator, the ECG equipment output has the visual appearance approximating a human ECG signal.
Accordingly, ECG signal simulators must be capable of generating a signal having multiple features. Moreover, the ECG signal simulator is preferably capable of proving ECG signals at different heart rates (i.e. the frequency at which the ECG waveform repeats). Further, it is preferable if ECG signal simulators can also simulate respiratory signals, at least in a rudimentary manner.
While devices having such capabilities are available on the market, such devices have tended to be large, bulky, and complex. For example, a common design involves storing digital samples forming an ECG waveform. When the device is used, the samples are sequentially retrieved from memory and provided to an analog output, which results in an ECG waveform signal output. One drawback to this design is that in order to store waveforms for multiple heart rates using a sufficient sample rate, the device may need to store thousands of samples. Storing thousands of samples for multiple cardiac waveforms often requires a separate memory device, which can increase cost, weight and power consumption.
It is preferable that such devices be cordless (e.g. battery-operated) to allow for better portability, ease of use, and reduced weight. However, the complex circuitry used for prior art simulators can have relatively high power consumption, which results in reduced battery life and inconvenience. There is a need, therefore, for an ECG signal generator/simulator that has reduced size and power consumption.